Dose titration of moxidectin oral gel against gastrointestinal parasites of ponies

Abstract

Moxidectin was tested as an oral gel formulation during a controlled test performed to evaluate dosages against equine gastrointestinal parasites. Four groups of ten ponies were used. Ponies ranged from 1 to 20 years of age and were naturally infected in southern Louisiana or Mississippi. Fecal exams and fecal cultures were performed on all ponies to determine the strongyle egg counts and the percent distributions of large and small strongyles. Following these determinations, ponies were allocated to replicates of four ponies to provide an even distribution of strongyle infection, age, weight and gender. Members of each replicate were then randomly assigned to one of four treatment groups. The doses tested were 300, 400 and 500 μg kg −1 body weight. The oral gel vehicle alone served as control. Treatments were administered behind the tongue and the ponies were observed continuously for 4 h for any adverse reactions; thereafter, ponies were observed at least twice daily. Necropsy examinations were performed 14 days post-treatment for the recovery and identification of any parasites present. Moxidectin, at all doses tested, was 100% efficacious against adults of Strongylus vulgaris, Strongylus edentatus, Triodontophorus spp. and 22 species of small strongyles. Moxidectin was also 100% efficacious against larvae of Strongylus edentatus and Oxyuris equi, greater than 94% efficacious against Strongylus vulgaris larvae and Oxyuris equi adults at 14 days post-treatment. Moxidectin proved highly efficacious against luminal small strongyle larvae (>99.9% against L 4 and >92% against L 3) and moxidectin demonstrated some efficacy against encysted small strongyle larvae as well. Although control ponies were not uniformly infected with Habronema muscae, Trichostrongylus axei and Parascaris equorum, none of these parasites were recovered from moxidectin-treated ponies, suggesting high efficacy against these species as well. Efficacy against Gasterophilus spp. was 89%, 96% and 97% in a dose-dependent fashion. Moxidectin had no demonstrable activity against Anoplocephala perfoliata.